The invention relates to a radiation device with at least one infrared radiator and at least one additional radiator with at least two elongated envelope tubes joined together which are permeable to light and infrared radiation and sealed from the ambient atmosphere, at least a first one of which has an incandescent coil filament which is electrically connected with an external power supply through sealed tube ends and external contacts, as well as to its use and a method for the treatment of surfaces.
In GB Patent 1544551 an electrical heat radiator is disclosed which has two heating coils disposed parallel to one another, each being arranged in a quartz glass tube, the quartz glass tubes being connected in their length by fusion. The two incandescent coil filaments are connected in series.
Even though a considerable increase of intensity can be achieved, only a comparatively narrow spectral range of the short-wave infrared radiation is emitted, it being difficult, as a rule, to dry rapidly and simultaneously paints and pigments and their solution for example in water after surface application, as for example by printing on a support.
Furthermore, EP 0 428 835 A2 and its corresponding U.S. Pat. No. 5,091,632 also disclose infrared radiators with twin tube radiators.
Furthermore, DE 198 39 457 A1 discloses the use of an infrared radiator with a carbon ribbon as heating element; such a carbon ribbon is suitable especially for the emission of IR radiation in a medium wavelength range of 1.5 to 4.5 xcexcm.
The invention is addressed to the problem of creating a thermal radiation device in order to dry rapidly coatings or impressions made with pigments or paints in solvents which are applied to surfaces, and at the same time to cause the solvents, such as toluene or water, to evaporate rapidly.
The problem is solved as regards apparatus by the fact that at least a second envelope tube is provided which has a radiating ribbon which is electrically connected to the power supply or to an additional external power supply through sealed ends and external contacts. The second envelope tube is likewise provided for the emission of infrared radiation, especially for the emission of IR radiation in the medium IR range. Of course, a different kind of temperature radiator which emits radiation in the medium IR range can also be used instead of the radiating ribbon. It has proven advantageous for the device to have comparatively great radiation components both in the visible spectral range and in the near infrared radiation range, especially with a wavelength ranging from 780 nm to 1.4 xcexcm, as well as in the medium IR radiation range from 2.5 xcexcm to 5 xcexcm.
In a preferred embodiment of the invention an elongated carbon ribbon is used as the radiating strip, the carbon ribbon being configured as an elongated coil in another preferred embodiment. It emits radiation in a medium IR spectral range, while an incandescent coil radiator emits short-wavelength IR radiation (near IR) and in some cases also visible light.
It proves to be especially advantageous that, by combining radiation sources with different temperatures (xcex94xcexmax greater than 400nm) in a common radiation device, the efficiency of processes for heat treatment can be improved over conventional short-wavelength IR radiation sources. For example, the efficiency of paint drying processes is improved.
On account of its superimposition of different Planck distributions, the radiation device has a greater percentage of IR radiation components than former radiation sources with only one temperature in the stated wavelength ranges.
In another advantageous embodiment, it is possible to provide, in addition to thermal radiation sources, at least one additional elongated tube permeable to light and UV radiation, which has an electrical discharge portion and an additional UV radiation in the wavelength range from 150 nm to 380 nm, which is especially suitable for drying paint.
Preferred embodiments of the infrared radiator and radiation device are disclosed herein
A special advantage over single radiators is reduced space requirement, and optimum radiation conditions can be created by the selective operation of the radiation sources with different wavelengths that are best for the particular fields of application.
A solution of the problem for a particular application is provided by the use of a twin-tube radiation device with an incandescent coil as the short-wave infrared radiation source and a tube provided with a carbon ribbon for the radiating strip as a medium-wave IR radiator.
The problem is solved, in a method for the treatment of surfaces with IR radiation, wherein especially coated or imprinted surfaces on substrates, or dissolved pigments on a support, are irradiated to dry them, by treating the surface at least for a time with an IR radiation with a high content in a first wavelength range of 780 nm to 1.2 xcexcm and simultaneously for a time with an IR radiation with a high content in a second wavelength range of 2.5 xcexcm to 5 xcexcm.
Advantageous embodiments of the method are disclosed herein.
In a preferred embodiment of the method, the surface radiation of the first wavelength range and of the second wavelength range overlap at least for a time, the first IR radiation being emitted from a radiator with an incandescent coil and the second IR radiation from a carbon ribbon as radiation source. It proves to be especially advantageous for the superimposition of the first and second wavelength ranges to have a spectral radiation distribution with a relatively great content in the wavelength range of 780 nm to 3.1 xcexcm.
An important advantage is to be seen in the fact that, depending on the embodiment, the individual radiation percentages of this radiation device can be turned on in an OR operation or in a common kind of switching. In the operation of machines with alternating processes, this results in the advantage that radiator alternation need no longer take place. Also, the user no longer needs different individual radiation sources, so that a smaller stock of replacement parts is achieved. Furthermore, the carbon radiator used can be used as a starting current limiter for the short-wave radiator (incandescent coil).
In an additional embodiment, the infrared spectra superimposed on the ultraviolet radiation content. Here, again, separate and common types of operation can be combined.